1. Field of the Invention
The present invention relates to a corneal surgery apparatus for ablating a cornea by irradiating a laser beam and an apparatus for determining a corneal ablation amount.
2. Description of Related Art
There is known a corneal surgery apparatus which ablates a cornea by irradiating a laser beam and changes a shape of the cornea in order to correct a refractive error of an eye. The apparatus of this kind ablates part of the cornea so as to remove a lens component corresponding to a correction amount from the cornea. At this time, when only an optical region (hereinafter referred to as an “optical zone”) which secures the correction amount is ablated, a boundary between an ablation area and a non-ablation area appears as a height difference. Therefore, in order to smoothly connect (join) the optical zone and the non-ablation area, the applicant has proposed, in Japanese Patent Application Unexamined Publication No. Hei6-189999 corresponding to U.S. Pat. No. 5,445,633, a method for forming an adjustment region (hereinafter referred to as a “transition zone”) outside the optical zone. By way of example, in the case of a myopic correction, a transition zone is determined by obtaining a circle inscribed in both of pre-operative and post-operative corneal shapes.
Further, in the case of a spherical correction or cylindrical correction of high degree of myopia, as one method for avoiding an ablation depth from being deep (great), a method of dividing the correction amount into a plurality of amounts and changing each ablation size (diameter) is performed. By way of example, as shown in FIG. 9, for a patient's eye (eye to be operated on) of which a spherical correction of myopia is S-5.00D (diopter), a method of dividing the correction amount into three stages is performed.
As described in Japanese Patent Application Unexamined Publication No. Hei6-189999 corresponding to U.S. Pat. No. 5,445,633, owing to the formation of the transition zone outside the optical zone, the height difference at the boundary between the ablation area and the non-ablation area is reduced, and a favorable result is obtained. However, according to the method provided in Japanese Patent Application Unexamined Publication No. Hei6-189999 corresponding to U.S. Pat. No. 5,445,633, especially in the case where the correction amount is large, a radius of the circle inscribed in both of pre-operative and post-operative corneal shapes becomes small, and a number of parts where a corneal curvature suddenly varies are tend to appear over a wide range of the transition zone. If there are a number of parts where the corneal curvature suddenly varies, there is a problem that they cause a glare or a halo in night vision.
Also, in the method as shown in FIG. 9, there is a tendency of that the corneal curvature suddenly varies at the boundary of each of the stages. In addition, since it is necessary to manually input the correction amount and the ablation size (diameter) for each of the stages, there are such problems of that the inputting is laborsome, an error in inputting is apt to occur, the number of the divided stages is limited because of the manual inputting, an appropriateness of inputting depends on experiences of an operator, and the like. Furthermore, there is a problem of that, in the case of a surgery divided into a plurality of the stages, surgical time becomes longer.